There are a variety of types of applications in which there is a need to control temperatures and/or temperature gradients within a structure being cooled. One example is phased array antenna systems, which are used in a number of different contexts, such as satellites and other space vehicles. A phased array antenna system includes an array of antenna elements that are separately controlled by respective circuit portions. Wavefronts transmitted and received by the antenna system are represented electrically by respective signals at the various antenna elements, and these electrical signals have phases which typically vary from antenna element to antenna element across the array. Consequently, it is important that the circuit portions associated with respective antenna elements introduce equal amounts of phase delay into the signals passing through them. Variations in the phase characteristics of the different circuit portions are undesirable, because such variations can introduce distortion into transmitted wavefronts and received wavefronts.
The circuit portions used to control the antenna elements in existing phased array antenna systems have phase characteristics that inherently vary with temperature. Consequently, in order to avoid undesirable phase variations between electrical signals in the circuit portions for different antenna elements, it is desirable that all of the circuit portions for all of the antenna elements operate at substantially the same temperature. In other words, it is desirable to avoid any significant temperature gradients across the array.
Various cooling techniques have previously been developed to attempt to avoid temperature gradients across the circuitry of phased array antenna systems. Some approaches utilize a single-phase or two-phase coolant which is mechanically pumped. However, mechanically pumping these coolants requires an external source of energy to drive the pump, and the use of a mechanical pump presents reliability concerns as a result of the possibility of a mechanical failure. The reliability considerations are of particular concern with respect to environments such as a space vehicle, where repairs can be difficult or impossible.
A different approach uses heat pipes. However, since a phased array antenna system typically has a two-dimensional array of antenna elements, heat pipes represent a one-dimensional attempt to solve a two-dimensional problem. In particular, a layer of parallel heat pipes can be provided to transport high heat fluxes in directions parallel to the heat pipes, but it is not possible to distribute heat in a transverse direction without adding a second layer of heat pipes that extends transversely to the first layer. The second layer of heat pipes increases the size and weight of the system, and is not as effective as the first layer in distributing heat, due to the conductive resistance between the two layers of heat pipes. In a phased array antenna system in which the circuitry is provided in a configuration commonly known as a slat architecture, the use of even a single layer of heat pipes may be difficult or impossible, due to dimensional limitations inherent in the system.